1. Field of the Invention
This invention relates to ventilation ductwork used in air conditioning and heating systems, and more particularly concerns an automatically adjusting damper device adapted to equalize internal and external air pressures upon initiation of air movement within the ductwork.
2. Description of the Prior Art
In air conditioning and heating systems, air is generally blown through a ventilator duct from the air conditioner or furnace, and is pulled back through return ducts. Upon initial activation of the blower fan, a positive pressure is generated within the ventilator ducts and a vacuum is pulled in the return ducts. Subsequent to a brief period of start-up of the blower, the pressure inside the return duct equalizes with the ambient pressure outside. Due to the large volumes of air moved by the blowers in large systems, the vacuum generated may be sufficient to cause deformation or implosion of return ducts. Such damage is costly to repair in terms of materials and manpower and once repair has been made, the damage is likely to recur. It is therefore desirable to provide means in existing ductwork to alleviate the damaging effects of internal vacuum.
Various damper devices have earlier been disclosed for use in ductwork. However, such devices are usually designed to open or close duct passages either manually or through some mechanical or electromechanical means. Damper devices of this nature may be used to divert air to various locations within a structure or simply to close-off a passageway when the blower is deactivated. U.S. Pat. No. 4,262,652, for example is intended to close off air passage from a furance when the furnace is not activated. The damper is mounted within the duct and in the form of a butterfly valve. It has a spring loaded open position and is driven closed by an electric motor. This and other similar devices require electrical connection, utilize a number of moving parts, restrict airflow within the duct and are difficult to install.
U.S. Pat. Nos. 4,290,552 and 4,017,028 disclose similar dampers driven to open and closed positions by means of thermostatic control units, springs and convoluted bimetalic coils. These devices require periodic temperature adjustment in usage and could only be used for one of heating or air conditioning applications concurrently. Moreover, none of these devices are designed to equalize internal and external pressures of the duct.
It is therefore a primary object of the present invention to provide a self adjusting damper device to equalize momentary pressure differences occurring between the interior and exterior of heating/air conditioning ductwork upon start-up of the associated blower fan.
It is another object of the present invention to provide a damper device of the aforesaid nature which may be easily installed in various orientations in existing ductwork without restricting airflow within the ductwork.
It is yet another object of the present invention to provide a damper device of the aforesaid nature which has minimal moving parts, is self-contained, and requires no outside electrical, mechanical or pneumatic activation mechanism.
It is still another object of the present invention to provide a damper device of the aforesaid nature which is of durable construction and amenable to low cost manufacture.